We are currently investigating the potential usefulness of the rhesus rotavirus MMU18006 strain developed as a vaccine candidate at the Laboratory of Infectious Diseases (NIAID). This virus is a simian rotavirus strain derived from a stool of a 3.5 month old rhesus monkey with acute diarrhea. In the phase I study the vaccine was administered in two different doses 100 thousand or 10 thousnad pfu which represented a 1/100 or 1/1000 dilution of RRV-1 respectively), to 35 infants (4-10 months old). A third group comprised 18 infants received placebo. The study was carried out in a double-blind fashion. The infants were examined daily for presence of side reactions. Rectal temperature was taken twice a day by medical personnel and stool specimens were collected daily and analyzed for rotavirus shedding. Significant reactions were not observed in the infants who received either dose of the vaccine when compared to the placebo group. A low incidence of fever, loose stools (including 3 cases of diarrhea) and upper respiratory symptoms were observed; however, these symptoms and signs were as common in the placebo group as in the immunized children. We have recently examined the serum samples obtained from the 53 children. Serological assays performed for rotavirus antibody included complement fixation assay, immune adherence hemagglutination assay, plaque reduction neutralization assay and a tube neutralization assay. Overall, 65% of the vaccinated children developed a seroresponse; 76.5% of the children receiving the high dose (1:100 dilution of the original vaccine stock) had a response compared to 53% of those receiving the lower dose (1:1000 dilution). For the phase II study, approximately 100 infants will be vaccinated. 100 additional infants will receive placebo in a double-blind fashion.